There has been a long-term desire to measure the height of family members within the home environment. This is especially true in households with one or more growing children. In an effort to track growth, it has been typical for families to manually mark a child's (or other person's) height on a wall, using for example, a ruler, a book, or other flat object in an attempt to make a projection from a top of the child's head to the wall.
There are at least two problems associated with this sort of procedure for tracking height. First, the height marks, by being made on the wall, may eventually wear away or need to be painted over, making the wall an impractical means of storing a child's growth progress as a possible keepsake. Secondly, as it can be difficult to keep the ruler, book, or other flat object perpendicular to the wall and aligned on the top-most portion of their head and thus get a truly accurate marking of his/her height.